In recent years, various types of heat pipes have been used due to their efficient heat transmission, their light weight and simple structure, and their quick responsiveness to heat. Referring to FIG. 4, there is shown one example.
Referring to FIG. 4 (a), a working liquid (2) is sealed under decompression in a rigid, sealed pipe (1) that is cylindrical in shape and has a diameter of less than a hundred millimeters. Working liquid (2) is evaporated at one end of sealed pipe (1), and the vapor is condensed at the other end. This allows a large amount of heat to be transferred even if there is only a slight temperature difference. The working liquid (2) that is liquefied at the condensation section is circulated back to the evaporation section by the capillary action of a wick (3). In place of wick (3), straight grooves can be formed on the inner wall surface of sealed pipe (1) so that the capillary action of the straight grooves can circulate working liquid (2).
Heat pipe (4) as described above is used in mechanical devices such as exhaust heat recovery devices and heat exchangers. The heat transfer properties can also be used in cancer thermotherapy and for cooling CPUs in notebook computers. Referring to FIG. 4 (b) and (c), there is shown an example of how the heat pipe can be used in CPU cooling. A heat pipe (4a) is extended from a CPU (6) and bent in the shape of an L, with the bent section being disposed near a hinge of a notebook computer 7. Another heat pipe (4b) bent in the shape of an L is disposed next to heat pipe (4a) near the hinge and they are fixed together by a metal sheet (5) wrapped around them. Heat pipe (4b) is extended along the back surface of a liquid crystal display panel (7a), and the heat generated by CPU (6) is transferred to the back surface of the panel and dissipated.
To simplify the bending of heat pipe (4), it would be possible to use a roller or the like to radially compress a coil wrapped around the outer perimeter surface of sealed pipe (1). Alternatively, a roller blade can be rolled along the outer perimeter surface of the sealed pipe so that a helical groove is formed on sealed pipe (1), thus making deformation easier.
Even if bending is made easier by a helical groove formed on heat pipe (4), the grooves cannot be formed adequately deep. Thus, the flexibility of heat pipe (4) is inadequate and the pipe can spring back during bending, making the operation difficult. Also, when heat pipe (4) is used for cooling the CPU of a notebook computer, two heat pipes (4a) and (4b) must be joined at the hinge section, thus decreasing the thermal efficiency. Furthermore, since heat pipe (4) is rigid, the bond between the heat pipes becomes worn when liquid crystal display panel (7a) is bent repeatedly, thus shortening the life span.